It is known that among the most common forms of cancer which affects humans, skin cancer is without doubt one of the most widespread. In particular, in the last twenty years, the incidence of skin cancer has increased remarkably. Part of this increase is due to the fact that, for the typical person, the amount of time exposed to solar radiation, both natural and artificial, has increased. In addition, solar radiation has become less filtered due to the concomitant decreases in the ozone layer. Overexposure of skin to solar radiation has contributed to the increasing use of sunscreens. However, the sunscreens themselves may be subjected to photolytic reactions induced by light, resulting in the formation of free radical species that are harmful to healthy skin.
It is known that the ultraviolet component of solar radiation (UV rays) plays a primary role in inducing skin tumours since these UV rays directly attack cells, damaging their DNA. Owing to the spectral distribution of solar UV, the UVA (380-315 nm) component of sunlight is now believed to be the main cause of photoageing and photocarcinogenesis and is much more effective than UVB (315-280 nm) in inducing peroxidative damage. Consequently, most skin care cosmetic products now include UVA filters in their formulations along with UVB filters, and separately include antioxidants such as vitamin E to deactivate free radicals (e.g., reactive oxygen species (ROS) such as superoxide, hydroxyl, nitric oxide, and peroxyl) generated during UVA exposure.
Modern sunscreens should provide and maintain their initial UV absorbance, and hence protection of skin, throughout the entire period of exposure to sunlight. However, not all UVA and UVB filters are sufficiently photostable. For example, simple in vitro assays show that there is a decrease in the spectral absorbance of most commonly used UV filters and that this largely correlates with increased UVA-induced lipid peroxidation. The magnitude of this effect is affected by the specific UV absorber used, whether it is used alone or in combination, and whether other antioxidants are present.
The addition of antioxidant agents into sunscreen creams is known and in many cases includes categories of compounds such as vitamin E and ascorbic acid. Other antioxidant compounds which have been used for this purpose includes the class of cyclic mono-nitroxide radicals, such as, for example 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO), and 2,2,6,6-tetramethylpiperidine-3-hydroxy-1-oxyl (TEMPOL). These are both cyclic aliphatic nitroxides. Another class of antioxidant includes the nitroxide bis(2,2,6,6-tetramethyl-1-oxyl-piperidine-4-yl)sebacate, which appears to be a more efficient photo-antioxidant than vitamin E.
Many cosmetic creams containing sun filters or cosmetic creams which are currently available contain a plurality of antioxidant agents and coformulants. However, the use of antioxidant agents in a cream containing sun filters or in a cream for dermatological and/or cosmetic purposes has various complications and disadvantages.
A first disadvantage is that once applied to the skin some compounds, including antioxidants, could themselves be subjected to degradation due to sun rays with the consequent formation of reactive oxygen species. The free radicals formed are themselves harmful to the skin, cells, and cellular components such as lipids, proteins, and nucleic acids. Furthermore, the free radicals formed can chemically react with other radicals or coformulants present in the sun cream.
Another disadvantage of existing products is due to the fact that when the number of compounds, or antioxidant agents used in a cosmetic cream is increased, it becomes increasingly difficult to prepare a product in which the beneficial characteristics of the compound is stable over time.
Yet another disadvantage of existing products is due to the fact that upon increasing the number of compounds or antioxidant agents used in a cosmetic cream, it becomes increasingly difficult to prepare a product with characteristics of high compatibility in relation to the various skin types on which it will be applied. In fact, it may happen that the topical application of a cream containing a sun filter, or a cosmetic cream, induces certain allergic reactions due to the specific chemical composition of the product.
Furthermore, another disadvantage is that increasing the number of active antioxidant agents used in the preparation of a cream containing a sun filter, or a cosmetic cream, increases the costs of the final product.
Therefore, it would be highly desirable to have at one's disposal a new antioxidant or class of antioxidant compounds that overcomes these disadvantages of the presently utilized products and methods. In particular, it would be desirable to be able to have at one's disposal a single hypoallergenic sunscreen compound that possesses high efficacy UV blocking activity, and antioxidant activity but that is also chemically stable over time.